Blower assembly with motor integrated into the impeller fan and blower housing constructions

ABSTRACT

A blower comprises a blower housing, a fan, a motor and a support member. The blower housing has an air outlet opening. The fan is within the blower housing, the fan is adapted for rotation about a fan axis. The motor has a stator and a rotor. The rotor is rotatably coupled to the stator for rotation about the fan axis. The rotor and fan are coupled such that the fan rotates with the rotor. The support member is connected between the stator of the motor and the blower housing and extends generally radially from the fan axis. The support member supports both the motor and the fan.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to a blower assembly for an air handlerin which an electric motor is integrated into the constructions of theimpeller fan and the blower housing of the blower assembly. Morespecifically, the present invention pertains to a blower assembly inwhich an axial flux motor has its stator integrated into theconstruction of the blower housing of the assembly and has its rotorintegrated into the construction of the impeller fan of the assembly.

2. Description of Related Art

The typical construction of a blower assembly for an air handler, forexample as a furnace, includes a fan that is rotated by an electricmotor and a blower housing that contains the fan.

The typical blower housing is comprised of a scroll-shaped outer walland a pair of side walls that are connected to opposite sides of thescroll-shaped outer wall. The outer wall has opposite ends that arepositioned on opposite sides of an outlet opening of the blower housing.The side walls are also positioned on opposite sides of the outletopening. The side walls have circular, coaxial holes through the sidewalls that function as air inlet openings of the blower housing.

The motor is typically mounted to one of the blower housing side walls.The shaft of the motor is coaxial with the center axes of the blowerhousing inlet openings. This positions the motor either directlyadjacent one of the side wall inlet openings, or in some constructions,the motor extends through the side wall inlet opening into a portion ofthe motor housing interior.

The impeller fan is mounted to the motor shaft in the blower housinginterior. The typical impeller fan has a circular plate at one axial endof the fan or at an intermediate portion of the fan that is connected tothe motor shaft.

The common blower assembly construction described above includesfeatures that detract from the efficiency of the blower assembly.Positioning the motor adjacent or partially extending into one of theair inlet openings of the blower housing restricts the air flow throughthat inlet opening and thereby contributes to the inefficiency of theblower assembly. Additionally, the circular plate of the impeller fanthat connects the fan to the motor shaft restricts the free flow of airthrough the interior of the impeller fan and thereby also contributes tothe inefficiency of the blower assembly.

SUMMARY OF THE INVENTION

The blower assembly of the present invention overcomes disadvantagesassociated with the constructions of conventional blower assemblies byhaving the construction of the motor integrated into the constructionsof intermediate portions of the impeller fan and the blower housing.This eliminates the prior art positioning of the motor adjacent one ofthe blower housing inlet openings or extending through one of the blowerhousing inlet openings and thereby eliminates the inefficienciesassociated with this prior art positioning of the motor. In addition,the portion of the motor integrated into the fan construction includes acylindrical hub with a center bore through the hub that balancespressure and the free flow of air through the interior of the fan.

The blower housing of the invention comprises a scroll-shaped outer wallhaving a length with opposite first and second ends that are positionedat opposite sides of the outlet opening of the housing. The housing alsocomprises a pair of side walls that are secured to the opposite sides ofthe scroll-shaped outer wall. The side walls have circular holes thatare coaxially aligned and function as the air inlet openings of theblower housing. The novel construction of the blower housing of theinvention includes an interior wall. The interior wall is parallel tothe side walls and is secured stationary to the interior surface of thehousing outer wall at a centered position between the two side walls.The interior wall has a circular hole through the wall that is coaxialwith the air inlet openings of the two side walls.

The motor of the blower assembly is mounted to the interior wall of theblower housing. This eliminates the inefficiencies associated with theprior art positioning of the motor adjacent an air inlet opening of theprior art blower housing or extending into the air inlet opening of theprior art blower housing. Although other motor types which have shortaxial lengths could be used, the preferred motor is an axial flux motorhaving a circular stator construction integrated into the constructionof the interior wall at the hole through the wall. The wiring associatedwith the stator and the control systems of the motor are run through oralong the interior wall to the exterior of the blower housing. The rotorof the motor includes a hollow cylindrical hub that is mounted forrotation by one or more bearings inside the stator. The hub has a pairof annular plates connected to the axially opposite ends of the hub. Theplates extend radially outwardly from the center hub over opposite sidesof the interior wall. The magnets of the motor are secured to at leastone of the plates.

The impeller fan of the blower assembly is comprised of a pair ofcentrifugal or squirrel-cage fans. These fans may have different widthdimensions for air flow purposes. The fans are positioned on theopposite sides of the interior wall and are connected to the pair ofplates that extend radially from the cylindrical hub of the rotor.

The blower assembly of the invention described above has no obstructionsto the free flow of air through the inlet openings of the blower housingside walls into the interior of the fan contained in the blower housing.The blower assembly also has a smaller size than comparable prior artblower assemblies that have motors that project out from one side oftheir blower housings. This enables the blower assembly of the inventionto be used in a narrower air handler enclosure. This is accomplished bythe positioning of the motor in the interior of the housing on theinterior wall of the housing. Employing the axial flux motorconstruction allows for the free flow of air through the interior of theblower housing between the two centrifugal fans. This eliminates theinefficiencies associated with prior art centrifugal fans due to thecenter plates of the fans restricting air flow through the fans.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention are set forth in the followingdetailed description of blower assemblies of the invention and in thedrawing figures.

FIG. 1 is a side elevation view of one side of a blower assembly of theinvention, with the opposite elevation view being a mirror image of FIG.1.

FIG. 2 is an end elevation view of the blower assembly from the left endof the blower assembly as shown in FIG. 1.

FIG. 3 is an upper, left perspective view of the blower assemblyrelative to the blower assembly as shown in FIG. 2.

FIG. 4 is an upper, right perspective view of the blower assemblyrelative to the blower assembly as shown in FIG. 2.

FIG. 5 is a left perspective view of the blower assembly relative to theblower assembly as shown in FIG. 2.

FIG. 6 is a right perspective view of the blower assembly relative tothe blower assembly as shown in FIG. 2.

FIG. 7 is a lower, left perspective view of the blower assembly relativeto the blower assembly as shown in FIG. 2.

FIG. 8 is a lower, right perspective view of the blower assemblyrelative to the blower assembly as shown in FIG. 2.

FIG. 9 is a partially sectioned view of the blower assembly showingportions of the blower housing, fans and motor and showing the interiorwall in its entirety.

FIG. 10 is a view similar to that of FIG. 9, but from the opposite sideof the blower housing as shown in FIG. 9.

FIG. 11 is an end elevation view of the blower assembly as shownpartitioned in FIGS. 9 and 10.

FIG. 12 is a schematic representation of one embodiment of the blowerassembly of the invention.

FIG. 13 is a schematic representation of a further embodiment of theblower assembly.

FIG. 14 is a schematic representation of a further embodiment of theblower assembly.

FIG. 15 is a schematic representation of a further embodiment of theblower assembly.

FIG. 16 is a schematic representation of a further embodiment of theblower assembly.

FIG. 17 is a schematic representation of a further embodiment of theblower assembly.

FIG. 18 is a schematic representation of a further embodiment of theblower assembly.

FIG. 19 is a side elevation of a further embodiment of the blowerassembly.

FIG. 19 a is a section view taken through the plane of line 19 a-19 a ofFIG. 19.

FIG. 19 b is an enlarged fragment view of FIG. 19 a, showing motorfeatures.

FIG. 19 c is a perspective view of the motor of the blower assembly ofFIG. 19.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The blower assembly of the present invention is basically comprised of ablower housing 12, a fan 14 contained inside the blower housing, and amotor 16.

The blower housing 12 has an outer wall 18 having a scroll-shaped lengththat extends from a first end edge 22 of the outer wall to an oppositesecond end edge 24 of the outer wall. As best seen in drawing FIGS. 3-8,the outer wall first end edge 22 forms the cutoff of the blower housing.Additionally, the first 22 and second 24 end edges of the outer wall 18define opposite sides of a rectangular outlet opening 26 of the blowerhousing.

The blower housing also includes first 28 and second 32 side walls. Asseen in the drawing figures, portions of the peripheries of the two sidewalls 28, 32 are connected to the opposite sides of the outer wall 18.The first 28 and second 32 side walls also have respective straight edgeportions 34, 36. The straight edge portions 34, 36 of the two side wallsare also positioned at opposite sides of the blower housing outletopening 26 and with the outer wall first end edge 22 and second end edge24 define the rectangular configuration of the outlet opening. Each ofthe side walls 28, 32 is also provided with a circular hole 38, 42through the side wall. The circular holes 38, 42 are coaxially alignedand function as the air inlet openings of the blower housing 12.

An interior wall 44 of the blower housing 12 is shown in FIGS. 5-11. Theinterior wall 44 is a flat, planar wall having a circular center hole 46through the wall. The interior wall 44 is secured to the interiorsurface of the blower housing outer wall 18 and is positioned in theinterior of the blower housing 12 parallel to the side walls 28, 32. Theinterior wall center hole 46 is coaxial with the inlet openings 38, 42in the respective side walls 28, 32. The hole 46 through the wall 44allows a balance of air pressure and air flow on opposite sides of theblower housing interior. In alternate embodiments, the wall 44 could bereplaced by a ring having the center hole 46 with the ring connected tothe housing interior by three or more circumferentially spaced spokes orwebs. In addition, the interior wall 44 is shown in the drawing figurescentered in the blower housing 12 relative to the side walls 28, 32. Inalternate embodiments of the invention, the interior wall 44 could bepositioned off center in the blower housing 12 and more toward one orthe other of the side walls 28, 32. Optimum efficiency is achieved whenthe interior wall concept is employed in a high efficiency blowerhousing such as those described in pending patent application Ser. Nos.11/935,726; 12/178,161 and 12/631,415; all of which are incorporatedherein by reference.

The motor 16 of the blower assembly is an axial flux motor. The stator52 of the motor is integrated into the construction of the housinginterior wall 44 at the center hole 46 through the wall. The interiorwall 44 can be constructed in such a manner that allows for the wiringassociated with the stator 52 and the control systems of the motor 16 tobe run through the interior of the interior wall 44. Alternatively, thewiring can be run across the exterior surface of the interior wall 44.The stator windings 54 extend radially inwardly from the interior wall44 into the center hole 46. In the illustrated embodiment of the blowerassembly, the stator has thirty six slots and eighteen windings 54. Therotor 56 of the motor includes a hollow cylindrical hub 58 having a bore62 through the hub 58. The hub 58 is mounted by bearings on the stator52 for rotation of the hub 58 inside the stator 52. A pair of first andsecond annular plates 64, 66 project radially outwardly from theopposite ends of the hub 58 over opposite sides of the stator 52 andopposite sides of the interior wall 44. The hub interior bore 62 definescenter holes through the plates 64, 66. The hub interior bore 62 and theholes through the plates 64, 66 are all coaxially aligned with the inletopenings 38, 42 through the respective side walls 28, 32 of the blowerhousing 12. The permanent magnets 68 of the rotor 56 are secured to theinterior surface of at least one of the plates 64, 66 that opposes thestator windings 54. In the illustrated embodiment thirty magnets areemployed on the rotor 56. In alternate embodiments of the blowerassembly, permanent magnets could be provided on both of the plates 64,66. The circular peripheral edges 72, 74 of the respective plates 64, 66are secured to the fan 14 of the blower assembly. In addition, the motor16 need not be positioned at the center of the blower housing interiorand could be positioned to either side of the interior by relocating theinterior wall 44 supporting the motor 16.

The impeller fan 14 of the blower assembly is comprised of a firstcentrifugal or squirrel-cage fan 76 and a second centrifugal orsquirrel-cage fan 78. The two fans 76, 78 are basically the same inconstruction. As shown in FIGS. 9-11, the first fan 76 is connected tothe peripheral edge 72 of the first annular plate 64 and the second fan78 is connected to the peripheral edge 74 of the second annular plate66. This connects the two fans 76, 78 to the rotor 56 with the fanspositioned on opposite sides of the blower housing interior wall 44. Onoperation of the motor 16, the rotor 56 rotates freely relative to thestator 52 and drives the fans 76, 78 in rotation relative to the blowerhousing interior wall 44 and the blower housing 12.

The bore 62 through the stator hub 58 allows for the balancing ofpressure between the interiors of the two fans 76, 78. The bore 62 alsoallows for the free flow of air between the interiors of the two fans76, 78 and the two sides of the blower housing interior on oppositesides of the interior wall 44.

The blower assembly constructed in the manner above has no obstructionsto the free flow of air through the inlet openings of the blower housingside walls into the interiors of the fans contained in the blowerhousing. The blower housing assembly also has a smaller size thancomparable prior art blower assemblies have motors projecting from oneside of their blower housings. This enables it to be used in a narrowerair handler enclosure. This is accomplished by positioning the motor inthe interior of the blower housing on the inner wall of the housing.

FIGS. 12-18 are schematic representations of the possible positioning ofcontrols 82 for the motor 16 of the blower assembly and the wiring 84 orother electronics communicating the controls with the motor.

In FIG. 12 the motor controls 82 are shown mounted to the exterior ofthe blower housing outer wall 18. The wiring 84 for the stator 52extends through the interior of the housing interior wall 44. In otherembodiments, the housing interior wall 44 could be replaced by acircular ring with a center opening that supports the motor 16 in thesame manner as the interior wall 44, with the ring being secured to theinterior of the blower housing outer wall 18 by a plurality of spokes orwebs spatially arranged around the ring and extending radially from thering to the blower housing outer wall 18. In this variant embodiment,the wiring 84 would extend through one of the radially extending spokesor webs. The wiring 84 extending through the interior wall or one of thespokes or webs provides EMI shielding of the wiring.

FIG. 13 is a representation of the controls 82 being mounted on theblower housing interior wall 44 or one of the interior spokes or webs.In this arrangement the controls 82 are contained in a housing having aflat or aerodynamic shape so as not to obstruct air flow. The wiring 84runs through the interior of the interior wall 44 to the motor 16, orthrough one of the spokes or webs used as an alternate to the interiorwall 44. Power and signal connections to the controls 82 would alsoextend through the interior wall 44 or supporting spoke or web to theexterior of the blower housing 12.

FIG. 14 represents the motor controls 82 being mounted on the exteriorof the blower housing 12. A heat sink 86 for the controls 82 extendsthrough the blower housing 12 to the interior of the blower housing foraccess to cooling air. The wiring 84 for the stator 52 extends throughthe interior wall 44 or through one of the alternative spokes or websdirectly to the controls 82. If the wiring is routed through theinterior of the blower housing 12, it must be positioned to be protectedfrom the blades of the fan 14. In addition, some EMI shielding of thewiring would likely be required. With the controls 82 positioned on theexterior of the blower housing 12, the power and signal cables for thecontrols are easily accessible.

FIG. 15 is also a representation of the controls 82 being mounted on theexterior of the blower housing 12 with a heat sink 86 extending into theblower housing. In the arrangement shown in FIG. 15, the controls 82 arenot an integral part of the interior wall 44 supporting the motor 16 asshown in FIG. 12. Here again, with the controls 82 positioned on theexterior of the blower housing 12, the power and signal cables areeasily accessible.

FIG. 16 is a representation of a blower arrangement where the motor issupported by a stationary shaft and the controls 82 being mounted in thecenter hub 84 of the motor construction, thereby closing the center hubbore 62. A hollow, stationary shaft 88 extends through the motorcontrols 82 and supports the motor controls in the interior of theblower housing 12. The shaft 88 is connected to the blower housing 12 bythree circumferentially spaced rods 92 that connect one end of the shaft88 to the blower housing 12 and three circumferentially spaced rods 94that connect the opposite end of the shaft 88 to the blower housing 12.The motor stator 52 is also attached to the stationary shaft 88. Thus,in the construction represented in FIG. 16, there is no need for theinterior wall 44 in the blower housing 12. The power and signalconnections for the controls 82 would be routed through the interior ofthe shaft 88 to the exterior of the blower housing 12.

FIG. 17 represents a further arrangement where the center bore 62 isobstructed by the controls 82 positioned at the center of the stator 52.As in the previously-described embodiments, the stator 52 is supportedin the blower housing 12 by the interior wall 44, or by the alternativespokes or webs. The power and signal connections for the motor controls82 are routed through the interior of the interior wall 44, or throughthe interior of one of the alternative spokes or webs.

FIG. 18 is a representation of an arrangement where the motor stator 52is mounted to one side of the blower housing 12 and the motor rotor 56is mounted to one side of the fan 14 adjacent the stator. The motorcontrols 82 are mounted to the stator 52 at the side of the blowerhousing 12. One end of the fan 14 is supported by bearings 96 positionedbetween the fan and the stator 52. The opposite end of the fan 14 isconstructed with a center ring 98 and three spokes 102 that extendradially from the ring to the fan. A bearing 104 mounts the fan ring 98on a shaft 106. The shaft 106 is held stationary to the blower housing12 by three rods 108 that connect the shaft 106 to the housing.

FIGS. 19-19 c show a blower assembly 110 similar to the blower assemblyof FIGS. 1-11, but with the center brace being a fin-shaped mount 144instead of the interior wall 44. For simplicity, the reference numbersfor the elements of the blower assembly 110 are the same ascorresponding elements of the blower assembly of FIGS. 1-11 except thereference numbers for the blower assembly 110 contain the prefix “1”.The fin-shaped mount 144 supports the motor 116 and the blower housing112. The fin-shaped mount extends radially from an arcuate portion(shown in FIG. 19 c) of the outer periphery of the stator 152. An endportion of the mount 144 extends radially from the blower housing 112.The mount end portion is configured for supporting the motor controlcircuit 182. Preferably, the mount 144 includes a removable cover member144 a for enclosing the motor control circuit. Referring to FIGS. 19 band 19 c, the permanent magnets 168 of the rotor 156 are arranged toform a magnet ring. Each magnet 168 includes an inner edge 168 a and anouter edge 168 b (see FIG. 19 b). The inner edges 168 a combine togenerally define an inner circumference of the magnet ring. The outeredges 168 b combine to generally define an outer circumference of themagnet ring. The diameter of the outer circumference is represented asD_(o) and the diameter of the inner circumference is represented asD_(i). Preferably, the ratio of the diameters of the outer and innercircumferences D_(o), D_(i) is not more than approximately 1.2.Preferably, the blower assembly 110 has nothing obstructing the twoinlet openings 138, 142.

In view of the foregoing, it should be appreciated that the inventionachieves several advantages over prior art blowers.

As various modifications could be made in the constructions hereindescribed and illustrated without departing from the scope of theinvention, it is intended that all matter contained in the foregoingdescription or shown in the accompanying drawings shall be interpretedas illustrative rather than limiting. Thus, the breadth and scope of thepresent invention should not be limited by any of the above-describedexemplary embodiments, but should be defined only in accordance with thefollowing claims appended hereto and their equivalents.

It should also be understood that when introducing elements of thepresent invention in the claims or in the above description of exemplaryembodiments of the invention, the terms “comprising,” “including,” and“having” are intended to be open-ended and mean that there may beadditional elements other than the listed elements. Moreover, use ofidentifiers such as first, second, and third should not be construed ina manner imposing any relative position or time sequence betweenlimitations.

What is claimed is:
 1. A blower comprising: a blower housing having anair outlet opening; a fan within the blower housing, the fan beingadapted for rotation about a fan axis, the fan comprising a first set ofimpeller blades and a second set of impeller blades, the first set ofimpeller blades being spaced axially from the second set of impellerblades; a motor having a stator and a rotor, the rotor being rotatablycoupled to the stator for rotation about the fan axis, the rotor and fanbeing coupled such that the fan rotates with the rotor; and a supportmember connected between the stator of the motor and the blower housingand extending generally radially from the fan axis, the support membersupporting both the motor and the fan, the support member being betweenthe first set of impeller blades and the second set of impeller blades.2. A blower as set forth in claim 1 wherein the rotor includes an outerdiameter and an axial length, the axial length extending along an axialextent of the fan axis, the axial length of the rotor being not morethan approximately one-half of the outer diameter of the rotor.
 3. Ablower as set forth in claim 2 wherein the axial length of the rotor isnot more than approximately one-quarter of the outer diameter of therotor.
 4. A blower as set forth in claim 2 wherein the support memberdoes not extend axially beyond the axial extent of the fan axis.
 5. Ablower as set forth in claim 1 comprising a single bearing, the bearingtransmitting load between the rotor and the stator and transmitting loadbetween the fan and the blower housing.
 6. A blower as set forth inclaim 5 wherein the motor comprises an axial flux motor.
 7. A blower asset forth in claim 1 wherein the support member comprises a wallextending radially outward from adjacent the stator to adjacent theblower housing.
 8. A blower as set forth in claim 7 wherein the wallcircumscribes the stator.
 9. A blower as set forth in claim 1 whereinthe support member comprises a fin-shaped mount extending radially froman arcuate portion of the outer periphery of the stator.
 10. A blower asset forth in claim 1 wherein the fan extends along a fan axial extent ofthe fan axis, and wherein the motor is generally axially centered in thefan axial extent of the fan axis.
 11. A blower as set forth in claim 1wherein the rotor of the motor comprises a plurality of magnets arrangedto form a magnet ring, each of the plurality of magnets having an inneredge and an outer edge, the inner edges of the magnets combining togenerally define an inner circumference and an inner diameter of themagnet ring, the outer edges of the magnets combining to generallydefine an outer circumference and an outer diameter of the magnet ring,the outer diameter of the magnet ring being not more than approximately1.2 times the inner diameter.
 12. A blower comprising: a blower housinghaving an air outlet opening; a fan within the blower housing, the fanbeing adapted for rotation about a fan axis; a motor having a stator anda rotor, the rotor being rotatably coupled to the stator for rotationabout the fan axis, the rotor and fan being coupled such that the fanrotates with the rotor; and a support member connected between thestator of the motor and the blower housing and extending generallyradially from the fan axis, the support member supporting both the motorand the fan.
 13. A blower as set forth in claim 12 wherein the rotorincludes an outer diameter and an axial length, the axial lengthextending along an axial extent of the fan axis, the axial length of therotor being not more than approximately one-half of the outer diameterof the rotor.
 14. A blower as set forth in claim 12 wherein the axiallength of the rotor is not more than approximately one-quarter of theouter diameter of the rotor.
 15. A blower as set forth in claim 12wherein the support member does not extend axially beyond the axialextent of the fan axis.
 16. A blower as set forth in claim 12 comprisinga single bearing, the bearing transmitting load between the rotor andthe stator and transmitting load between the fan and the blower housing.17. A blower as set forth in claim 16 wherein the motor comprises anaxial flux motor.
 18. A blower as set forth in claim 12 wherein thesupport member comprises a wall extending radially outward from adjacentthe stator to adjacent the blower housing.
 19. A blower as set forth inclaim 18 wherein the wall circumscribes the stator.
 20. A blower as setforth in claim 12 wherein the support member comprises a fin-shapedmount extending radially from an arcuate portion of the outer peripheryof the stator.
 21. A blower as set forth in claim 12 wherein the fanextends along a fan axial extent of the fan axis, and wherein the motoris generally axially centered in the fan axial extent of the fan axis.22. A blower as set forth in claim 12 wherein the rotor of the motorcomprises a plurality of magnets arranged to form a magnet ring, each ofthe plurality of magnets having an inner edge and an outer edge, theinner edges of the magnets combining to generally define an innercircumference and an inner diameter of the magnet ring, the outer edgesof the magnets combining to generally define an outer circumference andan outer diameter of the magnet ring, the outer diameter of the magnetring being not more than approximately 1.2 times the inner diameter. 23.A blower comprising: a blower housing having an air outlet opening; afan within the blower housing, the fan being adapted for rotation abouta fan axis; an axial flux motor having a stator and a rotor, the rotorbeing rotatably coupled to the stator for rotation about the fan axis,the rotor and fan being coupled such that the fan rotates with therotor; and a support structure operatively connecting the stator of themotor to the blower housing.
 24. A blower as set forth in claim 23comprising a single bearing, the bearing transmitting load between therotor and the stator and transmitting load between the fan and theblower housing.
 25. A blower as set forth in claim 23 wherein the fan isintegrally connected to the rotor.
 26. A blower comprising: a blowerhousing having an air outlet opening; a fan within the blower housing,the fan being adapted for rotation about a fan axis, the fan extendingalong a fan axial extent of the fan axis; and a motor having a statorand a rotor, the rotor being rotatably coupled to the stator forrotation about the fan axis, the rotor and fan being coupled such thatthe fan rotates with the rotor, the rotor including an outer diameterand an axial length, the axial length extending along a rotor axialextent of the fan axis, the axial length of the rotor being not morethan approximately one-half of the outer diameter of the rotor, themotor being generally axially centered in the fan axial extent of thefan axis.